Nucleic Acid Testing (NAT) is a subset of molecular diagnostic markers, based on testing for the presence of a nucleic acid sequence in a sample, associated with a certain condition (most often a clinical pathology). The sample could be a body fluid, a tissue sample, a body secretion or any other sample obtained from a patient which could contain the targeted nucleic acids.
Traditionally, NAT diagnosis has been used for the diagnosis of infectious diseases. Particularly, it has been used for the diagnosis of HIV, Hepatitis C Virus (HCV), Hepatitis B Virus (HBV), Chlamydia trachomatis, Neisseria gonorrhoeae and Mycobacteria tuberculosis. In recent years NAT diagnosis has expanded to noninfectious diseases, for example, for the diagnosis of prostate cancer based on DD3 (PCA3). DD3 (PCA3) is a very prostate cancer-specific gene. It has shown a great diagnostic value for prostate cancer by measuring quantitatively the DD3 (PCA3) transcript in urine sediments obtained after prostatic massage. DD3 (PCA3) is a non-coding transcript, therefore diagnosis in the protein level is not possible. More NAT markers for more cancers in addition to prostate cancer are currently pursued.
NAT diagnostic markers have at least four advantages on protein based diagnostic modalities:                1. They are likely to be more sensitive and specific (as has been shown for diagnostic kits for HIV and HCV). This finding could be related to at least two things:                    a. The test analyte could be amplified (e.g. with PCR)            b. The detection method is sequence specific rather than epitope specific                        2. They allow diagnosis even if a differentially expressed transcript is non-coding (as in the case of DD3 (PCA3))        3. The research tools for the discovery of novel NAT markers are much more advanced and robust than for protein markers (e.g. advanced DNA chip technology compared with protein chip technology)        4. NAT analytes are sometimes found in body secretions and/or body fluids and therefore could replace the need for a tissue biopsy when a serum marker is not available.        
However, NAT markers suffer from a few disadvantages including:                1. The analyte itself is quite an unstable molecule (certainly when compared with a protein).        2. The analyte itself is by nature not physiologically secreted, therefore it is not always easily found in samples.        
NAT markers development for noninfectious diseases was not pursued for a long time, which was mostly a result of expensive and not fully developed detection methods on one hand and intellectual property barriers on the other. With the advance in technology and expiration of key patents in the field, the industry is investing more and more resources in that direction and it seems that NAT based tests are going to be much more prevalent for noninfectious diseases in the future.